Here is my free advice to HID: Stop it. Be the leaders you are. Be the leaders the industry needs.
Threatening that warranties will not be valid is embarrassing. It is coming off as desperate. Worse, you are letting your defensiveness blind you, and you are missing a fantastic opportunity.
The truth is, you've been out-innovated here, your moat with readers has eroded, and your last-ditch effort is to threaten. The problem is, you are threatening the wrong people with this message: your customers. By declaring that the readers warranty will be voided if an end-user decides to use one of these plug-in solutions, you are harming the exact people you think you are helping: the end user. Threatening and using a scare tactic to alarm your customers and impede innovation is an old and tired way to mitigate competitiveness.
It is a bad look.
Instead, show some vulnerability and self-awareness as an organization and lead. Evolve your business. Respect your customers' choices and embrace the technology being built off of your platform. You have the perfect opportunity here to be just that: a platform. Sure it is scary, and there are many unknowns but fear the devil you know (old business models) and lean into the devil you don't know (new business models).
Look at your readers as an extension of Mercury. Instead of looking to do everything seed to flower, offer your readers as a platform. Shoot, go all in and call it "the industries open reader platform."
Instead of fighting technology evolution by using scare tactics, put the customer at the center, and help accelerate innovation. You have the right and the permission to participate (also known as charging for it and making $) in the value generation, but don't let the desire to defend the hill you have already lost get in the way of a beautiful idea and progress.
Show some leadership.